Various types of wireless sensor network have been proposed. Among these, the so-called Body Area Network or BAN is an example of wireless personal area networks (WPANs), used to convey information over relatively short distances.
Unlike wireless local area networks (WLANs), connections effected via WPANs involve little or no infrastructure. This feature allows small, power-efficient, inexpensive solutions to be implemented for a wide range of devices. Of particular interest is the possibility of the medical BAN (MBAN) in which sensors are used to monitor the status of one or more patients. A BAN employing mainly sensors for feeding sensed data to a data sink is an example of a wireless sensor network (WSN); however, more active devices, such as actuators, may be also be included in a MBAN.
Standard IEEE 802.15.4 defines the physical layer (PHY) and medium access control (MAC) sublayer specifications for low data-rate WPANs. IEEE 802.15.4 has some similarities with a standard for higher data-rate WPANs, IEEE 802.15.3. The documents IEEE Std 802.15.4-2006 and IEEE Std 802.15.3-2003 are hereby incorporated by reference in their entirety.
WPANs of the type envisaged in IEEE 802.15.4 are suitable for applications such as industrial monitoring, but do not offer the kind of data reliability required for MBANs. In medical applications, there is a requirement to reduce the costs associated with human labour while increasing the reliability and process automation and reducing human error. Sensors can provide the required intelligence, and already are widely employed in medical equipment. This includes hospital recuperative care, home care, intensive care units and advanced surgical procedures. There are many different types of sensors employed for medical applications, including external sensors for pulse, temperature etc., sensors which come in contact with body fluids, sensors used in catheters (through incision), sensors for external applications, disposable skin patches with wireless sensors, and implantable sensors.
A WPAN of one or more sensors around each of the patients in a hospital or medical ward could provide multiple clinical benefits including patient mobility, monitoring flexibility, extension of monitoring into care areas that are currently unmonitored, reduced clinical errors and reduced overall monitoring costs. Body worn sensors may include various sensor types on a single patient body. They require a capability to be applied or removed quickly from the patient's body.
On an individual basis, such sensors may have bit rates of as low as 1-2 kbps per patient and on an aggregate basis they may require a 10 kbps bit rate. A range of as little as a few meters may be adequate. However, medical WSN applications are mission critical applications in the clinical environment. Robust wireless links for bounded data loss and bounded latency, capacity for patient and sensor density, coexistence with other radios, battery life for days of continuous operations and small form factors for body worn devices, are among the requirements for medical WSNs or MBANs. These requirements can be satisfied through utilization of techniques such as diversity and error control techniques in the time and frequency domain, including Forward Error Correction (FEC) and Adaptive Repeat reQuest (ARQ), low duty cycle TDMA for sensor information rate, and more efficient small antennas.
Efforts are therefore in progress to define a further standard IEEE 802.15.6 which aims to define the properties of Body Area Networks, particularly for medical applications. One of the key requirements of IEEE 802.15.6 is high reliability for medical applications with low battery consumption. This is even more important for emergency situations where the lives of the patients depends on the reliability of wireless links in medical WSN applications. Existing standards such as IEEE 802.15.4 have been designed for commercial application with no consideration of such emergency life saving scenarios.
In particular, there is a need to ensure reliability of communications with network devices such as sensors involved in such an emergency situation, without increasing the power consumed by the network devices.